1. Field of the Invention
The present invention relates to shape measuring apparatus and method for eyeglass element, in particular, to the apparatus and method to measure shapes of a lens frame, a lens template, pattern, a demo lens and the like.
2. Description of the Related Art
In the prior art, a known shape measuring apparatus for eyeglass element traces the shape of a lens frame with a measuring element (contact element, feeler, stylus) by sliding the measuring element in a groove of an inner periphery of the lens frame. Japanese Unexamined Patent Application Publication No. 2002-36084 and No. 2002-98518 disclose such a shape measuring apparatus which aims not to deform easily deformable lens frames such as a thin lens frame or a half glass lens frame due to force from the measuring element at the time of measuring the shape the lens frames, by changing a rotation direction and speed of the measuring element.
Such a known shape measuring apparatus uses a DC motor or the like to drive the measuring element. However, there is a problem that the measuring element may hit a lens frame and damage it when getting in contact therewith since the speed of the moving measuring element is not controlled.
Another problem is that even when the DC motor is given a minimum amount of driving force to overcome friction of the moving measuring element for contacting the measuring element with the groove of the lens frame, the measuring element may move too fast, and hit the groove of the lens frame and bounce off from it.
For the purpose of preventing bouncing-off of the measuring element, the measuring element can be moved slowly. However, this may cause another problem that the measuring element stops moving halfway due to friction.
For measuring the shape of a lens template, the same problem that the measuring element hits the circumferential edge of the template and bounces off therefrom may occur.